UNDERSTANDING SPACIAL AND TEMPORAL PATTERNS OF WATER CHEMISTRY IN OTTER CREEK, NEW YORK

Establishing a baseline for water chemistry of a body of water is critical to understanding natural conditions and assessing potential impact from human activities in the future. Otter Creek, in Cortland County, New York, is a small stream located within a sole-source aquifer system. In this study, we evaluated the spatial and temporal characteristics of water chemistry in Otter Creek with focus on the 2,000 meter reach where the creek flows through the Cortland Water Works. The studied reach runs east/northeast and is joined at a confluence by an overflow path via a culvert. Weekly groundwater, precipitation, and surface water samples were collected at six sites along the channel from March to April, 2012 with additional sampling in September and October, 2012. Weekly flow measurements were also conducted at four locations in the spring, 2012. Water chemistry of collected samples was analyzed using Ion Chromatography.

Water chemistry in Otter Creek varied spatially with low concentrations of major cations (Na⁺, K⁺, Mg²⁺, and Ca²⁺) and anions (Cl^-, HCO₃^- and SO₄^2-) in upstream sampling sites and increased after the confluence due to an approximate 30% contribution from the overflow path supported by groundwater. A lack of mixing and variable water chemistry across the channel immediately downstream of the confluence suggests an additional source of water with contributions of up to ~60 kg/day of Na⁺ and ~150 kg/day of Cl^- to the creek, as well as indicates the presence of preferential flow paths in the channel. Temporal changes of water chemistry within the creek proved insignificant at most sites during the sampling period at low flow condition. However, in October 2012, the dissolved solute concentrations illustrated a quick response to precipitation, exhibiting a strong dilution following rainfall events. The significance of this study lies in the establishment of a baseline for monitoring within the creek and the city of Cortland’s drinking water supply as well as identifying an unknown source of water contributing to the creek using water chemistry.